The present invention relates to a hot melt ink thermal transfer recording sheet. More particularly, the present invention relates to a hot melt ink thermal transfer recording sheet useful for recording thereon clear dotted ink images with a high dot reproducibility, while the occurrence of missing or partial dots is prevented by using a hot melt ink thermal transfer printer provided with a thermal head.
2. Description of the Related Art
The basic mechanism of the hot melt ink thermal transfer recording is that an ink ribbon having a thermally fusible ink coating is superimposed on a recording sheet capable of receiving thereon the ink, the superimposed ribbon and sheets are pressed between a platen roll and a thermal head under an appropriate pressure, and a resistive exothermic member arranged in the thermal head generates heat in accordance with electric signals applied thereto so that the ink ribbon is locally heated imagewise and the melted ink images are thermally transferred to the recording sheet. In this thermal transferring operation, derived colored images can be obtained by superimposing single colored hot melt inks different from each other on each other.
The hot melt ink thermal transfer recording system has a simple mechanism and can be easily maintained. Therefore, this recording system is widely utilized as a printer of word processors and facsimile machines.
Recently, to obtain a higher continuous tone reproducibility of printed images than that of conventional dither systems, printing systems are now utilizing an area continuous tone image-forming system in which the size of individual printing dots is changed to provide multiple continuous tones of images or a color density continuous tone image-forming system in which the size of individual printing dots is not changed but the color density of the individual printing dots is changed to provide multiple continuous tones of images.
Also, the ink image-recording sheet is required to be able to accurately receive the hot melt ink dots with a high reproducibility in a full color recording system in wide range of from low energy applications to high energy applications.
When a conventional recording sheet is used for the area continuous tone printing system or the color density continuous tone printing system, to obtain the multiple continuous tone images, portions of the printed images applied with low energy are unclear because of frequent occurrence of missing and/or partial dots.
Under these circumstances, Japanese Unexamined Patent Publication (Kokai) No. 62-160,277 discloses an attempt to prevent printing errors such as missing or partial dots, by adding a silica pigment having a high oil absorption to the ink-receiving layer. However, when the silica pigment is fixed with a conventional binder, for example, water-soluble polymeric material or an aqueous emulsion of water-insoluble polymeric material, the resultant ink-receiving layer exhibits a low bonding strength and thus when the ink ribbon is peeled off from the recording sheet after the thermal transfer printing operation is completed, the transferred ink layer is separated together with the ink ribbon from the recording sheet. The reasons for this phenomenon are not completely clear. However, it is assumed that the conventional polymeric material is adsorbed in fine pores formed in the surface portions of the silica pigment particles.